1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor (hereinafter also simply referred to as “photoreceptor”) to be used in a printer, a copying machine, or a fax machine based on an electrophotographic system, as well as a method of producing the same and an electrophotographic device; and especially to an electrophotographic photoreceptor, which is able to exhibit superior resistance to abrasion, or stability in electrical properties owing to inclusion of a specific inorganic oxide in a photosensitive layer, as well as a method of producing the same and an electrophotographic device.
2. Background of the Related Art
An electrophotographic photoreceptor has a basic structure, in which a photosensitive layer having a photoconductive function is placed on a conductive substrate. An organic electrophotographic photoreceptor using an organic compound as a functional component responsible for generation or transport of electric charge has been recently studied actively and come to be used more and more in a copying machine, a printer, etc. in view of advantages of a great diversity of materials, high productivity, safety, etc.
Generally, a photoreceptor requires a function of retaining surface electric charge in a dark place, a function of generating electric charge by receiving light, and further a function of transporting the generated electric charge. As such a photoreceptor there are a so-called monolayer photoreceptor provided with a single layer of photosensitive layer having all of the functions, and a so-called stacked (functionally separated) photoreceptor provided with a photosensitive layer which stacks layers functionally separated into a charge generating layer mainly responsible for a function of generating electric charge upon receipt of light, and a charge transporting layer responsible for a function of retaining surface electric charge in a dark place, and a function of transporting electric charge generated upon receipt of light.
The photosensitive layer is generally formed by coating a coating liquid, in which a charge generating material, and a charge transporting material, as well as a resin binder are dissolved or dispersed in an organic solvent, on a conductive substrate. Especially, for a layer to constitute the outermost surface of an organic electrophotographic photoreceptor, polycarbonate, which is highly resistant to friction caused against paper or a blade for removing a toner, is superior in flexibility, and has high transparency for exposure light, is used frequently as a resin binder. Among others, a bisphenol Z polycarbonate is broadly used as a resin binder. Such a technology utilizing polycarbonate as a resin binder is described for example in Patent Document 1.
Further, due to increase in print quantity as the result of construction of a network in an office, or rapid expansion of light printing machine utilizing electrophotography, still higher resistance to abrasion, namely long-term durability, higher sensitivity, and higher responsiveness have come to be demanded recently for a printer according to an electrophotographic system.
Further, due to recent development and increase in the penetration rate of a color printer, increase in the printing speed, downsizing of a device, and reduction in number of parts have been advancing, and measures responding to various service environments have been also required. Under such circumstances, demand for a photoreceptor, which image characteristic or electrical property fluctuate little due to repeated use or fluctuation of service environment (room temperature, and environment), has been remarkably strengthening, and full satisfaction of such requirements by a conventional technology has become difficult.
For solving the problem, various methods for improving the outermost surface layer of a photoreceptor have been proposed.
Various polycarbonate resin structures have been proposed for improving the durability of a photoreceptor surface. For example, a polycarbonate resin containing a specific structure has been proposed in Patent Documents 2, and 3, however, the compatibility with various charge transporting agents or add-in materials, and the solubility of the resin have not been investigated sufficiently. Further, Patent Document 4 proposes a polycarbonate resin containing a specific structure, however in the case of a resin having a bulky structure there are many spaces among polymers and a discharging substance when electrified, a contact member, a foreign substance, etc. are apt to permeate into a photosensitive layer. Therefore, it is difficult to develop adequate durability. For the purpose of improvement of printing durability and coating property, Patent Document 5 proposes a polycarbonate having a special structure, however descriptions concerning a charge transporting material or an additive to be used in a combination are not sufficient, and there is a drawback in that stable maintenance of electrical properties over a long term use is difficult.
Patent Document 6 proposes addition of filler particles into a photosensitive layer for the purpose of improvement of resistance to abrasion, however an influence of aggregation of the particles in preparing a coating liquid for a photosensitive layer on photoreceptor characteristics, and on a method of producing particles, impurity control, and a surface treatment has not been examined adequately. Patent Document 7 proposes a charge transporting layer, in which pyrogenic silica is dispersed, however there is no description concerning the transparency of a slurry in which silica is dispersed in a solvent. Further, although there is a description concerning a metal element contained in silica in Patent Document 8, Patent Document 8 refers only to a technological basic idea with respect to existence or nonexistence of a contained metal element from the viewpoint of a factor of cost increase in production. There is no description concerning an impurity amount from the viewpoint of improvement of dispersibility.